Influence of Drake Passage oceanography on the parasitic infection of individual year-classes of southern blue whiting Micromesistius australis

Abstract

Southern blue whiting Micromesistius australis occurs around the southern coasts of South America and has been known to undertake summer feeding migrations to the Antarctic Peninsula and South Orkney Islands. The largest stock spawns to the southwest of the Falkland Islands and has been the subject of a major fishery on the Patagonian Shelf since 1978. Fish are infected with cysts of the Myxosporean parasite Kudoa alliaria which make the flesh commercially unattractive for fillets. A 10 yr study initiated in 1989 established that prevalence of the parasite is over 80% for fish older than 1 yr, and that average infection intensities are about 14 cysts per fish. We constructed a combined generalised linear/generalised additive model (GLM/GAM) of parasite abundance in M. australis. The combination of up to 30 ages and 8 yr of data spanning 10 yr allowed us to investigate rates of parasitism in 33 individual cohorts. Strong age and cohort effects in the model implied that the fish acquire parasites in their first 1 to 1 1 / 2 yr of life and that parasite abundance is set at these ages for the lifetime of the cohort. Several cohorts have statistically significantly lower parasite abundance than the majority, and these instances are roughly coincident with the 7 yr periodicity of seaice and sea surface temperature (SST) fluctuations in the Drake Passage. There are significant correlations between SST in the Drake Passage, the duration of sea-ice around Signy Island (South Orkney Islands) with a 1 yr time lag and parasite abundance in a cohort. We hypothesise that these correlations represent changes in the distribution and density of adult M. australis in warm and cold years, which thereby influences the density of the parasite field that juvenile fish encounter.

Variación geográfica de las comunidades de parásitos de la merluza de tres aletas Micromesistius australis al sur de Sudamérica

“…Al respecto, los taxapudieron ser adquiridos en un lugar muy diferente del lugar en que fueron capturados. Esta observación es en parte coherente con lo registrado por Agnew et al (2003) que sugieren una infección con K. alliaria antes de los dos años de edad, aunque la existencia de variaciones interanuales en la magnitud de este parasitismo no puede ser descartada.…”

“…Los antecedentes parasitológicos para esta especie son escasos e incluyen el registro del monogeneo Diclidophora micromesisti y del myxozoo Kudoa alliaria (Suriano & Martorelli 1984, Agnew et al 2003.…”

Segregation of SE Pacific and SW Atlantic southern blue whiting stocks: integrating evidence from complementary otolith microchemistry and parasite assemblage approaches

“…1), located in the SSW section of the Falkland Plateau, between 51 and 53°S (Agnew 2002). After spawning during September and October (Agnew 2002), adults disperse into feeding grounds located along the Patagonian shelf NE of the Falkland (Malvinas) Islands (Perrota 1982;Agnew 2002) or in Antarctic waters of the Scotia Sea (Bailey 1982;Barrera-Oro and Tomo 1988;Wöhler et al 2001;Agnew et al 2003). Here adults from both the SWA and the SEP spawning grounds might overlap (Céspedes et al 1998).…”

“…1) where they spawn in late winter, between mid July and mid September (Céspedes et al 1998;Lillo et al 2002;Saavedra et al 2007). Soon after, adults initiate a reverse (southward) migration, leaving Chilean waters in November (Céspedes et al 1998) to cross Drake's Passage (Agnew et al 2003) in search of summer feeding grounds ( Fig. 1), probably located in the Southern Scotia Sea (Bailey 1982).…”

“…In the present work, we conducted a preliminary study aimed to obtain, compare and integrate evi- Modified from Gordon (1991) based upon interpretations from Bailey (1982), Perrota (1982), Sánchez et al (1986), BarreraOro and Tomo (1988), Wiecaszek (1988), Cassia (2000), Agnew (2002), Agnew et al (2003), Saavedra et al (2007) and Arkhipkin et al (2009) dence about the stock structure and life history segregation of M. a. australis in Patagonia by using three complementary techniques: trace metals and stable isotopes in otolith cores (chemical tags), and parasite assemblages in adult tissues (biological tags). Otoliths have been shown to incorporate trace chemicals from early life, which can reflect habitat and physiological changes due to fish movements (Elsdon et al 2008).…”